Gut Microbes Prevent Locust Swarms

Migratory locusts are less likely to aggregate into crop-devastating swarms when infected by the parasite Paranosema locustae.

By Jef Akst | January 15, 2014

Locusta migratoria cinerascens (a different subspecies than addressed in Shi's research)WIKIMEDIA, HECTONICHUSSwarms of the migratory locust (Locusta migratoria manilensis) can wipe out thousands of hectares of crops grown in Africa and other parts of the world. But the key to preventing such devastating aggregation, researchers have learned, may be a simple gut parasite, Paranosema locustae.

According to a study published in PNAS this week (January 13), P. locustae bacteria prevent the release of swarming pheromones in the locusts’ scat, such that locusts coming into contact with scat from infected comrades were less likely to aggregate than those who were placed in chambers with scat from parasite-free insects.

Diving deeper into the mechanism of this anti-aggregation effect, entomologist Wangpeng Shi of China Agricultural University in Beijing and colleagues found that the bacteria caused an increase in acidity in the lower gut of the locusts, reducing levels of other microbes that are responsible for generating the aggregation-signaling pheromones. Moreover, infected insects expressed lower levels of serotonin and dopamine, neurotransmitters involved in swarming behavior.

The findings hold implications for the use of P. locustae in crop protection, coauthor Raymond St. Leger, a molecular biologist at the University of Maryland, College Park, told ScienceNOW. “People would like to use something biological that is environmentally safer than chemical insecticides,” he said. “The question now is whether we can create an easy chemical way to block these bacteria from producing pheromones or select for parasites that can keep the bacteria from flourishing in the gut.”

“This isn’t a silver bullet, but it is a big step forward,” added insect pathologist Stefan Jaronski of the US Department of Agriculture in Sidney, Montana, who was not involved with the work.